1. Field of the Invention
This invention relates to a fuel cell system including a fuel cell which gains electromotive force through an electrochemical reaction caused by the supply of a fuel gas containing hydrogen and an oxidizing gas containing oxygen, and to a freezing prevention method thereof
2. Description of the Related Art
It is assumed that a fuel cell is used under various conditions when the fuel cell is used as a power source for traveling, as in the case of using the fuel cell as a power source for an electric vehicle. Therefore, the fuel cell is required to operate appropriately under the any assumed conditions.
For example, in the case of using the fuel cell in cold climates, water present in the fuel cell freezes when an internal temperature of the fuel cell drops down to equal to or lower than 0 degrees (Celsius). To prevent the above-mentioned problem, an art which extracts the cooling water from the cooling water channel in the fuel cell when the fuel cell stops operating has been suggested (e.g., a Japanese Patent Laid-Open Publication No. HEI 6-223855). In the above structure, the cooling water does not freeze in the cooling water channel even when the internal temperature of the fuel cell drops down to equal to or less than 0 degrees after the fuel cell stops operating. Therefore, no problem is caused when activating the fuel cell next time.
However, an art for preventing water generated by the electrochemical reaction in the fuel cell from freezing in the fuel cell in cold climates had not been known conventionally. As the electrochemical reaction progresses in the fuel cell, water is generated on the cathode side of the fuel cell. The water is immediately generated when the fuel cell is activated and the electrochemical reaction is started. The generated water condenses in channels for oxidizing gas supplying around the electrodes and on the cathode side when the internal temperature of the fuel cell is low. In addition, the generated water may freeze when the internal temperature is equal to or less than 0 degrees.